The present invention relates to solid electrolyte capacitors with improved contact between carbon particles and conductive metal particles, as well as to methods for manufacturing the same.
The following is an explanation of a method for manufacturing a conventional solid electrolyte capacitor. First, a dielectric made of an oxide film is formed on the surface of a porous anode made of valve metal. A solid electrolyte is formed on this oxide film. After this, a cathode layer made of a carbon layer and a silver paste layer is formed, forming an internal element of a solid electrolyte capacitor. On the anode side, the lead of the anode is joined to an anode contact terminal, and on the cathode side, the internal element of the solid electrolyte capacitor is connected to a cathode contact terminal with a silver adhesive, and then the entire arrangement is molded with a packaging resin, thus obtaining a solid electrolyte capacitor.
In the above-described solid electrolyte capacitor, there is the problem that the equivalent series resistance (ESR) in the high-frequency range of the solid electrolyte capacitor cannot be decreased below a certain value, even when using manganese dioxide or a conductive polymer with an even higher conductivity as the solid electrolyte.
In JP 2858075B, manganese dioxide is used for the solid electrolyte. In this publication, the surface of the manganese dioxide is provided with protrusions and depressions, so that the surface of the carbon layer formed on the manganese is also provided with protrusions and depressions, and there is the problem that the contact area between the carbon layer and the silver paste layer is only at the protrusions of the carbon layer, so that the actual contact area becomes small. To address this problem, a conductive polymer layer is formed on the carbon layer by electrolytic polymerization. By forming the conductive polymer in the depressions of the carbon layer, the effective contact area of the carbon layer and the silver paste layer is increased, and a smaller equivalent series resistance in the high-frequency range is attained.
Furthermore, in JP H09-129512A, manganese dioxide is used for the solid electrolyte. As in the previous case, the surface of the manganese dioxide layer is provided with protrusions and depressions, so that the surface of the carbon layer formed on the manganese dioxide layer also is provided with protrusions and depression, and there is the problem that the effective contact area of the carbon layer and the silver paste layer becomes small. To address this problem, a metal layer made of a fine powder of gold, silver or palladium, or a mixture thereof is formed on the carbon layer, thus increasing the effective contact area of the carbon layer and the silver paste layer, and attaining a smaller equivalent series resistance in the high-frequency range.
Furthermore, in JP 2765462B, a conductive polymer is used for the solid electrolyte. In this publication, the surface of the conductive polymer layer becomes smooth, so that there is the problem that the adhesiveness between the conductive polymer layer and the carbon layer becomes poor. To address this, the surface of the conductive polymer layer is provided with protrusions and depressions, strengthening the adhesiveness between the conductive polymer layer and the carbon layer, and attaining a smaller equivalent series resistance.
However, in the above-described capacitors, the carbon particles or metal particles and the silver particles are in point contact between the carbon layer or metal layer on the carbon layer and the silver paste layer, so that there is the problem that the interface resistance between the carbon layer or metal layer on the carbon layer and the silver paste layer cannot be lowered, and the equivalent series resistance is large. In particular in view of the higher speeds of recent digital devices, there is a demand for capacitors with an extremely small equivalent series resistance, and attention has focused on the interface resistance at this portion.
In view of the foregoing, it is an object of the present invention to solve the problem of point contact between the carbon particles and the conductive metal particles by forming, in that order, a solid electrolyte layer, a carbon layer, and a conductive paste layer having numerous pores, and then forming a conductive polymer layer reinforcing the electric contact between the carbon particles of the carbon layer and the conductive metal particles of the conductive paste layer, which were in point contact.
That is to say, a solid electrolyte capacitor in accordance with the present invention includes an anode made of a valve metal on whose surface a dielectric oxide film layer is formed, a solid electrolyte layer formed on the dielectric oxide film, a cathode layer formed on the solid electrolyte layer, a cathode contact terminal electrically connected to the cathode layer, and an anode contact terminal electrically connected to the anode layer. The cathode layer includes a carbon layer containing carbon particles, and a conductive paste layer containing conductive metal particles and having numerous pores, formed in that order from the solid electrolyte layer side. The solid electrolyte capacitor further includes a conductive polymer layer formed through the numerous pores of the conductive paste layer and connecting the carbon particles of the carbon layer and the conductive metal particles of the conductive paste layer.
A method for manufacturing a solid electrolyte capacitor in accordance with the present invention includes a step of forming a dielectric oxide film layer on a surface of an anode made of a valve metal, a step of forming a solid electrolyte layer on the dielectric oxide film layer, a step of forming a cathode layer on the solid electrolyte layer, a step of electrically connecting a cathode terminal to the cathode layer, and a step of electrically connecting an anode terminal to the anode layer. The cathode layer formation step includes forming a carbon layer containing carbon particles and forming a conductive paste layer containing conductive metal particles and having numerous pores, in that order from the solid electrolyte layer side, and forming a conductive polymer layer formed through the numerous pores of the conductive paste layer and connecting the carbon particles of the carbon layer and the conductive metal particles of the conductive paste layer.